Author Topic: Charging a Capacitor and its Internal Resistance  (Read 1164 times)

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Offline AQUAMANTopic starter

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Charging a Capacitor and its Internal Resistance
« on: February 06, 2014, 03:37:15 pm »
As I understand, when you charge a capacitor, the initial voltage you see across it is due to its internal resistance.

So if you charge a capacitor with 1A, and it has 1Ohm internal resistance, the instantaneous voltage you see across it will be 1 Volt.

What I dont understand is if we made the internal resistance 10Ohms, then the voltage will be 10Volts. So we have charged the capacitor faster by somehow increasing the resistance? This doesnt make sense.

So my real question is to do with transistors. If above what I said was true, why not make MOSFETS with internal gate resistances of 80Ohms which would then begin to turn on instantly even if we only had 200mA into the gate - there would be absolutely no delay for the gate voltage to reach the threshold voltage. But surely, this cannot be the case.
 

Offline cyr

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Re: Charging a Capacitor and its Internal Resistance
« Reply #1 on: February 06, 2014, 04:04:37 pm »
Internal resistance is not magical. You can model it as an ideal capacitor in series with a resistor. Apply a current and you get an immediate voltage across the resistor, but that doesn't mean you have charged the cap.
 


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